1. Field of the Invention
Embodiments of the present invention generally relate to the preparation of supported catalysts for olefin polymerization. More particularly, embodiments of the present invention relate to supported dialuminoxane complexes capable of providing stable polymerization catalysts.
2. Description of the Related Art
Polymerization catalyst compounds are typically combined with an activator, also referred to as a co-catalyst, to form compositions having a vacant coordination site that will coordinate, insert, and polymerize olefins. Metallocene polymerization catalysts, for example, are typically activated with aluminoxanes. Aluminoxanes are generally oligomeric compounds containing —Al(R)—O— subunits, where R is an alkyl group. One common and widely used aluminoxane is methylaluminoxane (MAO).
There are several disadvantages to using MAO as an activator, however. First, the synthesis of MAO requires a complicated process. A typical synthesis includes the controlled hydrolysis of trimethylaluminum (TMA). This process must be precisely controlled to reduce losses of aluminum to insoluble species. Second, the starting material TMA is expensive and thus necessarily, the end product MAO is expensive. Third, a huge excess of MAO is needed relative to the metallocene to sufficiently activate the metallocene. Fourth, MAO has very low solubility in aliphatic solvents, which leads to poor storage stability since MAO tends to precipitates out of solution over time. Therefore, MAO is not a cost effective activator due to its problems of low yield, poor solubility, poor storage stability, and expensive reagents.
Alternative activators for metallocenes and other single-site polymerization catalysts have been discovered in recent years. For example, perfluorophenyl aluminum and perfluorophenyl boron complexes have been used. In EP 0 427 697 and EP 0 520 732, trisperfluorophenylborane was described as being capable of abstracting a ligand from cyclopentadienyl derivatives of transition metals while providing a stabilizing, compatible noncoordinating anion. However, the catalyst activity was not impressive.
There is a need, therefore, to provide a simpler method of co-catalyst synthesis and catalyst activation. There is also a need to improve catalyst economics by providing a highly active supported co-catalyst.